se#547  Move some products filter logic from SE to catalog QuerySet (#167)
se#547  Move some products filter logic from SE to catalog QuerySet (#167)

* se#547  Create QS.filter_by_categories method

* #164  Pdd issue for minor refactoring

* #164  Review#1 minor docstyle fix

fidals/refarm-site,fidals/refarm-site,fidals/refarm-site